# NCERT Physics Class 12 Exemplar Ch 5 Magnetism and Matter Part 1

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## Multiple Choice Type Questions

Q.1 A toroid of n turns, mean radius and cross-sectional radius a carries current . It is placed on a horizontal table taken as plane. Its magnetic moment

1. Is non-zero and points in the direction by symmetry.

2. Points along the axis of the toroid ().

3. Is zero, otherwise there would be a field falling as at large distances outside the toroid.

Q.2 The magnetic field of Earth can be modelled by that of a point dipole placed at the center of the Earth. The dipole axis makes an angle of with the axis of Earth. At Mumbai, declination is nearly zero. Then,

1. The declination varies between .

2. The least declination is

3. The plane defined by dipole axis and Earth axis passes through Greenwich.

4. Declination averaged over Earth must be always negative.

Q.3 In a permanent magnet at room temperature

1. Magnetic moment of each molecule is zero.

2. The individual molecules have non-zero magnetic moment which are all perfectly aligned.

3. Domains are partially aligned.

4. Domains are all perfectly aligned.

Q.4 Consider the two idealized systems: (i) a parallel plate capacitor with large plates and small separation and (ii) a long solenoid of length , radius of cross-section. In (i) is ideally treated as a constant between plates and zero outside. In (ii) magnetic field is constant inside the solenoid and zero outside. These idealized assumptions, however, contradict fundamental laws as below:

1. Case (i) contradicts Gauss’s law for electrostatic fields.

2. Case (ii) contradicts Gauss’s law for magnetic fields.

3. Case (i) agrees with .